Transmission level control system and method in radio communication station

Abstract: In a transmission level control system in a radio communication station where an in-station apparatus (201) is connected with an antenna site (101) through a transmission line (301), the in-station apparatus includes a plurality of burst carrier transmitters (BWT1-BWTm), and the antenna site comprises a level controller (102) for controlling the level of the carriers so as to compensate the received carriers for level reduction stemming from the transmission line. The in-station apparatus (201) further comprises a carrier combiner (203) for combining the transmitted burst carriers to transmit them to the antenna site through the transmission line, a selector (205) for selecting one of the burst carrier transmitters, and a controller (204) for activating the level control operation of the level controller (102) in the antenna site only when only the burst carrier transmitter selected by the selector outputs the transmitted carrier, otherwise inhibiting. In cases where there are some continuous carriers in the transmitted carriers, the level control operation is activated only when all the transmitted carriers are continuous carriers, otherwise inhibited.

Description: The present invention relates to transmission level control in radio communication, and more particularly, to a transmission level control system and method in a radio communication station where transmission carriers combine to be transmitted through a transmission line to an antenna site where transmission processing such as level control and power amplification is carried out to transmit them by radio. With the remarkable progress of the satellite communication technique in recent years, satellite communication has become vigorously utilized in various applications such as satellite broadcasting, public communication, and the like. With such a trend, there have been earth stations of various sizes and structures ranging from a large scale station for public communication, which is provided with an antenna of 10 meters in diameter, to a domestic satellite broadcast receiver. A large scale station, in general, employs an arrangement in which the communication apparatus placed within the station house is connected with the antenna site by a transmission line. A schematic arrangement of a transmission system in such an earth station is shown in Fig. 1. Referring to Fig. 1, the antenna site 1 is connected with the in-station apparatus 2 through the transmission line 3. Since the carriers received from the in-station apparatus 2 are subject to level reduction stemming from the transmission line 3, the antenna site 1 is provided with an automatic level control(ALC) circuit for controlling the carrier level so as to compensate the received carriers for the level reduction. Further transmission processing, such as conversion of the transmission frequency, is carried out, and the resulting carriers are amplified in power by means of a HPA (high power amplifier) to emit them from the antenna toward the satellite. Typically, such an earth station is required to combine a plurality of carriers for emitting them from a single antenna simultaneously. In the in-station apparatus 2, a multi-carrier controller 4 is comprised of a carrier combiner 5 for combining the carriers received from the burst carrier transmitters (BWT) with the carriers received from the continuous carrier transmitters (CWT). The combined carriers are transmitted to the ALC of the antenna site 1 through the transmission line 3 together with the calculated combined level of the carriers. The burst carrier and the continuous carrier mentioned above mean a short isolated sequence of modulated carriers and a continuous modulated carrier, respectively. The multi-carrier controller which combines various transmission carriers and calculates the combined level is disclosed in Japanese Patent publication no. JP 3 071 731 and Patent Abstracts of Japan vol. 15, no. 236 (E-1078) 18 June 1991. Using the transmission time of each carrier which is measured for each period of time, the controller performs an automatic power control such that the transmission output power is kept stable with the number of transmission carriers varying. According to the foregoing conventional transmission level control system, all the received carriers combine in the carrier combiner 5 to be transmitted to the ALC apparatus through the transmission line 3 regardless of whether a received carrier is a burst carrier or a continuous carrier, and based on that combined level, the automatic level control is performed by the ALC apparatus in the antenna site 1. However, since the burst carrier instantaneously varies in level, the level detection and the computation for level control become extremely complicated, resulting in complication of the level control operation and then a costly control system. An object of the present invention is to provide a transmission level control system and method which achieve a simple and low-cost level control for compensating the combined carriers for level reduction stemming from the transmission line connecting the in-station communication apparatus and the antenna site. The object is achieved by the features of the claims. In a radio communication station having an arrangement in which an in-station communication apparatus is connected with an antenna site through a transmission line, the in-station communication apparatus includes a plurality of burst carrier transmitters, and the antenna site is provided with a level controller for controlling the level of the carriers received from the in-station communication apparatus so as to compensate the received carriers for level reduction stemming from the transmission line. In a transmission level control system according to the present invention, the in-station communication apparatus is further comprised of a carrier combiner for combining the transmitted burst carriers to transmit the combined carriers to the antenna site through the transmission line; a selector for selecting one of the burst carrier transmitters; and a controller for activating the level control operation of the level controller in the antenna site only when only the burst carrier transmitter selected by the selector outputs the transmitted carrier. Preferably, the controller prevents the level controller from performing the level control operation but allows performing level amplification with the previous control gain when at least one transmitted burst carrier is output from a burst carrier transmitter other than that selected by the selection means. Since the level controller performs the level control operation in order to compensate the received carriers for level reduction stemming from the transmission line, the level control can be made based on the transmitted carrier output from the selected transmitter. In cases where there are some continuous carriers in the transmitted carriers, the level control operation is activated only when all the transmitted carriers are continuous carriers, otherwise inhibited. Fig. 1 is a schematic diagram illustrating a conventional transmission level control system in an earth station; Fig. 2 is a block diagram illustrating a specific embodiment of the transmission level control system according to the present invention; Fig. 3 is a block diagram illustrating a specific example of the carrier detecting circuit 204 according to the present embodiment; and Fig. 4 is a flow chart illustrating a control operation of the carrier detecting circuit 204 in the present embodiment. Referring to Fig. 2, an earth station has an arrangement where an antenna site 101 is connected to an in-station communication apparatus 201 through a transmission line 301. The antenna site 101 is comprised of an automatic level control (ALC) circuit 102, an effective-isotropically-radiated-power(EIRP) controller 103, an up converter(U/C) 104, and a high power amplifier(HPA) 105. The ALC circuit 102 automatically controls the level of the combined carriers received from the in-station apparatus 201 so as to compensate these carriers for level reduction stemming from the transmission line 301. The ALC operation is made by using the combined level calculated by a multi-carrier controller 202. However, the ALC operation is stopped by an ALC-OFF control signal of an ALC-ON/OFF control signal 302 received from the in-station apparatus 201 until an ALC-ON control signal is received. When the ALC-OFF control signal is received, the ALC operation is stopped, whereas the level amplification is carried out in the immediately preceding ALC condition or degree of amplification. The in-station apparatus 201 is comprised of the multi-carrier controller 202, a plurality of burst carrier transmitters BWT1 through BWTm, and a plurality of continuous carrier transmitters CWT1 through CWTn. The burst carrier transmitter emits a burst carrier modulated by a transmission signal as in voice communication. The multi-carrier controller 202 is comprised of a carrier combiner 203, a carrier detecting circuit 204, and an ALC selector 205. The carrier combiner 203 combines carriers received from the burst carrier transmitters BWT1 through BWTm and the continuous carrier transmitter CWT1 through CWTn to send out the combined carriers to the antenna site 101 through the transmission line 301. The carrier detecting circuit 204 transmits the ALC-ON/OFF control signal 302 to the ALC circuit 102. The ALC-ON/OFF control signal 302 is generated by the carrier detecting circuit 204 which detects the burst carriers BW1 through BWm emitted from the respective burst carrier transmitters BWT1 through BWTm, the continuous carriers CW1 through CWn from the respective continuous carrier transmitters CWT1 through CWTn, and connection signals DCS1 through DCSn from the respective continuous carrier transmitters CWT1 through CWTn. The ALC selector 205 emits a selection signal to the carrier detecting circuit 204, the selection signal indicating one burst carrier transmitter selected by, for example, an operator. Based on the burst carrier from the selected burst carrier transmitter, the ALC circuit 102 performs the ALC control. As illustrated in Fig. 3, the carrier detecting circuit 204 receives the burst carriers BW1 - BWm and the continuous carriers CW1 - CWn through a carrier receiver 2041. The received carriers are transferred to the carrier detector 2042 to detect which one of the transmitters is transmitting its carrier. Further, a connection detector 2043 detects which of the continuous carrier transmitters is sending its connection signal, and the detected result is sent to the carrier detector 2042. A determination controller 2044 receives the ALC-selection signal from the ALC selector 205 and the output of the carrier detector 2042 to determine whether to carry out the ALC control or not. According to this determination result, an ALC-ON/OFF controller 2045 transmits the ALC-ON/OFF control signal 302 to the ALC circuit 102. Next, the operation of this embodiment is described with reference to Fig. 4. On receipt of carriers, the carrier detector 2042 determines whether the received carriers consist of the burst carriers only or not (S401). If the received carriers include only the burst carriers, it is determined whether the received carrier is outputted only from the burst carrier transmitter selected by the ALC selector 205 or not (S402). If it is the selected burst carrier, the ALC-ON control signal is sent out to the ALC circuit 102 (S403). If not, the ALC-OFF control signal is sent out to the ALC circuit 102 (S404). If it is determined in step S401 that the received carriers include some continuous carriers, then it is further determined whether these carriers include some burst carriers or not (S405). If yes, the ALC-OFF control signal is sent out (S404) and, if these carriers include only continuous carriers, then the ALC-ON control signal is sent out (S403). To be more specific, a case in which the burst carrier transmitters BWT1 through BWTm are connected to the multi-carrier controller 202 for satellite communication is described. In that case, let us assume that a burst carrier transmitter BWTj is selected by the ALC selector 205 for ALC operation. If one of the burst carriers BW1 through BWm is input to the carrier detecting circuit 204, control is shifted to the next step S402 where it is determined whether this received carrier is the selected carrier BWj or not. If it is the carrier BWj, the ALC-ON control signal is emitted to the ALC circuit 102 of the antenna site 101 (S403). In this case, the ALC circuit 102 carries out the ALC control by using the calculated level of the burst carrier BWj received through the transmission line 301. On the other hand, if the received carrier is not the carrier BWj, the ALC-OFF control signal is emitted to the ALC circuit 102 (S404). In this case, the ALC circuit 102 stops the ALC control operation and amplifies the power with the immediately preceding gain. Next, if the received carriers include only the continuous carriers including no burst carriers, then the ALC-ON control signal is sent to the ALC circuit 102 (S403) so that the ALC operation is carried out as in conventional control by using the combined level of the continuous carriers. On the other hand, if the received carriers include both a burst carrier and a continuous carrier, then the ALC-OFF control signal is emitted to the ALC circuit 102 (S404). Therefore, the ALC operation is stopped to be followed by fixed amplification with the previous control gain.

Claims: A transmission level control system of a radio communication station having an arrangement in which an in-station communication apparatus (201) is connected with an antenna site (101) through a transmission line (301), the in-station communication apparatus comprising a plurality of burst carrier transmitters (BWT1 - BWTm), and the antenna site comprising a level controller (102) for controlling the level of carriers received from the in-station communication apparatus so as to compensate the received carriers for level reduction stemming from the transmission line, characterized in that : the in-station communication apparatus (201) further comprises: carrier combining means (203) for combining transmitted burst carriers to transmit combined carriers to the antenna site (101) through the transmission line (301); selection means (205) for indicating one of the burst carrier transmitters (BWT1 - BWTm); and control means (204) for activating the level-control operation of the level controller (102) in the antenna site when only the burst carrier transmitter selected by the selection means outputs a transmitted burst carrier. A transmission level control system as set forth in claim 1, wherein the control means (204) inhibits the leyel controller (102) performing the level control operation and level amplification is carried out in the immediately preceding level control condition or degree of amplification by an amplifier (105) of the antenna site (101) when at least one transmitted burst carrier is output from a burst carrier transmitter other than that selected by the selection means (205). A transmission level control system as set forth in claim 1, wherein the in-station communication apparatus further comprises a plurality of continuous carrier transmitters (CWT1 - CWTn) each emitting a demand connection signal only when communication is needed, the control means (204) is further for activating the level control operation of the level controller (102) in the antenna site when only the continuous carrier transmitters output the transmitted carriers. A transmission level control system as set forth in claim 3, wherein the control means (204) inhibits the level controller (102) performing the level control operation and level amplification is carried out in the immediately preceding level control condition or degree of amplification by an amplifier (105) of the antenna site (101) either when at least one transmitted burst carrier is output from a burst carrier transmitter other than that selected by the selection means or when the transmitted carriers include both at least one burst carrier and at least one continuous carrier. A transmission level control method in a radio communication station having an arrangement in which an in-station communication apparatus (201) is connected with an antenna site (101) through a transmission line (301), the antenna site comprising a level controller (102) for controlling the level of the carriers received from the in-station communication apparatus so as to compensate the received carriers for level reduction stemming from the transmission line, and the in-station communication apparatus comprising a plurality of burst carrier transmitters (BWT1 - BWTm), characterized by steps of: combining the transmitted burst carriers to transmit the combined carriers to the antenna site through the transmission line; indicating one of the burst carrier transmitters; and activating the level control operation of the level controller in the antenna site when only the burst carrier transmitter selected by a selection means outputs the transmitted burst carrier. A transmission level control method as set forth in claim 5, further comprising a step of inhibiting the level controller performing the level control operation and carrying out level amplification in the immediately preceding level control condition or degree of amplification by an amplifier (105) of the antenna site (101) when at least one transmitted burst carrier outputs from a burst carrier transmitter other than the selected transmitter. A transmission level control method as set forth in claim 5, wherein the in-station communication apparatus further comprises a plurality of continuous carrier transmitters (CWT1 - CWTn), and further comprises the step of: activating the level control operation of the level controller in the antenna site when only the continuous carrier transmitters output the transmitted carriers. A transmission level control method as set forth in claim 7, further comprising a step of inhibiting the level controller performing the level control operation and carrying out level amplification in the immediately preceding level control condition or degree of amplification by an amplifier (105) of the antenna site (101) either when at least one transmitted burst carrier is output from a burst carrier transmitter other than the selected transmitter or when the transmitted carriers include both at least one burst carrier and at least one continuous carrier.

Inventors: TAMANO CHINAMI, TAMANO, CHINAMI, TAMANO, CHINAMI, C/O NEC CORPORATION
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1994
Main classification: H04B7
IPC codes: H04B7, H04B1